This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application 2000-353197 filed on Nov. 20, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic pressure brake device for a vehicle. More particularly, the present invention pertains to a hydraulic pressure brake device provided with an assisting device (booster) for assisting the movement of a master cylinder in response to brake pedal operation.
U.S. Pat. No. 3,910,048 discloses a servomotor for use in a power braking system. As illustrated in FIG. 4, the servomotor 12 is provided with a pressure ratio changer. The servomotor 12 is further provided with a first piston 58 and a second piston 60 for transmitting an operative force to a master cylinder. The first piston 58 is connected to a wall 28 moved by a pressure differential. The second piston 60 is coaxially disposed within the first piston 58 and serves to transmit the input force which drives a control valve 71 for producing the pressure differential. The second piston 60 also operates a hydraulic lock valve 118 disposed within the master cylinder. When the first and second pistons 58, 60 are moved together in response to the movement of the wall 28, fluid is introduced into a lock chamber 114 via the lock valve 118. When the output force generated by the pressure differential reaches the maximum level, the simultaneous movement of the first and second pistons 58, 60 ceases. Further manual force input by the operator will move the second piston 60 disposed within the first piston 58 to close the lock valve 118 and hold the hydraulic fluid within the lock chamber 114 to prevent the first piston 58 from moving.
More particularly, when the first and second pistons 58, 60 are moved forward, hydraulic pressure is generated in each hydraulic pressure chamber 112, 146. The output from the first and second pistons 58, 60 follows a line 188 (shown in FIG. 5) until a second chamber 32 in the servomotor 12 reaches the atmospheric pressure level. At point 190 in FIG. 5, the input force from a brake pedal 20 is transmitted via a plunger 70 and a sleeve 66 to the second piston 60, wherein the second piston 60 is independently moved and a spring 130 is permitted to close a fluid passage 120. When the second piston 60 is further moved under the above-described condition, the output follows the line 192 in FIG. 5.
In the event the vacuum is unavailable, the second piston 60 is moved within the first piston 58 in response to the input force applied to a brake pedal 20, whereby the fluid passage 120 is immediately closed by the valve 118. The output under the above-described condition follows the line 196 in FIG. 5 which shows that a larger output can be generated than the output which can be generated when the first and second pistons 58, 60 are moved simultaneously under no power hydraulic pressure, which is represented by the line 195 in FIG. 5.
According to the servomotor 12 disclosed in the above U.S. Pat. No. 3,910,048, when the increased hydraulic pressure is locked in the lock chamber 114, the output follows the line 192 beyond a point 190 of the input force applied to the brake pedal 20 as shown in FIG. 5. When the assisting device malfunctions, including the case of no negative pressure or vacuum, the output follows the line 196 corresponding to the movement of the second piston 60 disposed within the first piston 58.
To achieve the operation described above, the servomotor 12 requires extensive modifications as compared to known servomotors to assure sufficient movement of the second piston 60 relative to the first piston 58. This may require re-designing the entire hydraulic pressure brake device, thus causing an increase in the cost associated with manufacturing the hydraulic pressure brake device. Further, a large diameter portion of the first piston 58 is slidably and movably disposed in a hydraulic pressure chamber of the master cylinder. The first piston 58 is slidably movable in an inner bore at a rear side of the master cylinder. Therefore, the above-described construction may result in an increase in the resistance by the sliding movement at the slidably moving portion.
Accordingly, the disclosed hydraulic pressure brake device is susceptible of certain improvements with respect to minimizing the required modifications of the assisting device to substantially maintain the master cylinder under a predetermined structure so as to assure desired input/output characteristics when the assisting device malfunctions. A need also exists for a hydraulic pressure brake device which is not as susceptible to difficulties associated with sliding movement at each slidably moving portion to thus improve the brake pedal operation feeling.
A hydraulic pressure brake device includes a master cylinder, a brake operating member, a master piston, a booster, a first auxiliary piston, a pressure transmitting chamber disposed between the first auxiliary piston and the master piston, a valve mechanism, and a second auxiliary piston. The master piston is provided in the master cylinder and is moved forward in response to an input force applied to the brake operating member. The booster is provided between the master cylinder and the brake operating member and assists the movement of the master piston in response to the input force applied to the brake operating member. The first auxiliary piston is disposed behind the master piston in the master cylinder and has a larger effective cross-sectional area than the effective cross-sectional area of the master piston. The valve mechanism is disposed in the first auxiliary piston for hydraulically sealing the pressure transmitting chamber when the movement of the master piston is assisted by the booster and for connecting the pressure transmitting chamber with a reservoir when the movement of the master piston is not assisted by the booster. The second auxiliary piston is disposed between the first auxiliary piston and the booster for transmitting the boosting power generated by the booster to the first auxiliary piston when the movement of the master piston is assisted by the booster, for transmitting the input force applied to the brake operating member to the valve mechanism, and for opening the valve mechanism when the movement of the master piston is not assisted by the booster.
The hydraulic pressure brake device also includes an output member and a rod. The output member is provided in the booster for transmitting the boosting power generated by the booster to the first auxiliary piston when the movement of the master piston is assisted by the booster. The rod is provided in the second auxiliary piston for transmitting the input force applied to the brake operating member to the valve mechanism and for opening the valve mechanism when the movement of the master piston is not assisted by the booster.
According to another aspect of the invention, a hydraulic pressure brake device includes a master cylinder, a brake operating member, a master piston provided in the master cylinder and movable in a forward direction in response to an input force applied to the brake operating member, a vacuum booster provided between the master cylinder and the brake operating member to assist the movement of the master piston in response to the input force applied to the brake operating member, a first auxiliary piston possessing a front portion disposed in the rearward opening bore of the master piston and having a larger effective cross-sectional area than the effective cross-sectional area of the master piston, a pressure transmitting chamber defined between the first auxiliary piston and the master piston, and a valve member disposed in a bore in the first auxiliary piston and engageable with a valve seat when the movement of the master piston is assisted by the vacuum booster to hydraulically seal the pressure transmitting chamber and disengageable from the valve seal when the movement of the master piston is not assisted by the vacuum booster for connecting the pressure transmitting chamber with a reservoir. A second auxiliary piston disposed between the first auxiliary piston and the vacuum booster to transmit the boosting power generated by the vacuum booster to the first auxiliary piston when the movement of the master piston is assisted by the vacuum booster and to transmit the input force applied to the brake operating member to the valve member to disengage the valve member from the valve seat when the movement of the master piston is not assisted by the vacuum booster.